The present invention relates to a device for adjusting a camshaft of an internal combustion engine.
Such a generic device is known from DE 196 11 641 C1. This publication according to the prior art describes the background to the invention, including the structural realization of the camshaft, its mounting and its cooperation with the internal combustion engine, which is not entered into in detail in the present application.
In practice, this known device according to the introductory clause shows how actuating means in the form of an electromagnetically driven tappet unit through cooperation with a lifting profile can cause an axial adjustment of the camshaft, predetermined by the course of the control groove, for instance with the purpose of associating a cam to different cam tracks in a switchable manner.
In such devices, presupposed as being known and generic, typically a plurality of tappets (actuating pins) are used, so that, according to the axial movement position of the lifting profile assembly, respectively a pin standing suitably opposite the control groove can engage and can cause the respectively intended axial movement.
At the same time, now newer internal combustion engines with variable valve drive, controlled by means of a sliding cam system, require compact shifting gates (i.e. as narrow as possible along an axial direction) as lifting profile assembly. This lies for example in that a distance between the roller cam followers for actuation of the valves is limited owing to a small cylinder distance and accordingly an axial length of the sliding cam on the camshaft is likewise restricted.
In the practical realization, this then leads in the case of such shifting gates, embodied in a compact manner (in which for instance the groove course—observed in an unwound manner—is S- or respectively Z-shaped) to the fact that, depending on the switching position, an individual tappet of the tappet unit projects axially over an end or respectively an edge of the lifting profile assembly. Basically, this is not a problem, however for instance owing to a faulty actuation of the actuating means (i.e. the correct individual tappet currently standing opposite the control groove is not actuated), but rather a neighbouring one, outside the covering with the lifting profile assembly) a tappet advance is caused, without this tappet (on further rotation of the lifting profile assembly) being able to be reset again. Typically, the generic camshaft movement principle, presumed as pre-characterizing, is namely based in that in fact electromagnetically advanced tappets engage in a suitable manner into the control groove, but a resetting (i.e. a returning) of the respective tappet takes place, however, in that the control groove, designed with groove depth that varies, drives the respectively advanced tappet back into the starting position again.
With the tappet (potentially faultily actuated as described above), because also in the respective operating state lying outside the lifting profile assembly, such a resetting is then, however, no longer possible, and for lack of other resetting mechanisms this problem then leads to a blockage or respectively defective situation, which can led to engine damage.
A possible solution to this problem consists in providing tappet units for the actuating means, which tappet means can be brought automatically (for instance also again electromagnetically) from the driven advance position back into the reset starting position again. However, this requires not only considerable additional structural expenditure in the realization of the actuators used for the actuating means, also again, with already limited installation space, such a solution would again produce additional disadvantages with regard to space.